Zoologger: The rat that defies powerful carcinogens

Zoologger is our weekly column highlighting extraordinary animals – and occasionally other organisms – from around the world

Species:Spalax ehrenbergiHabitat: Dark, suffocating tunnels in damp soil deep beneath you – if you happen to live in the eastern Mediterranean

As anti-cancer regimes go, this one isn't going to get many takers. The Middle East blind mole rat spends almost all of its 20 years of life hurrying down dark and fusty tunnels full of oxygen-deprived air. But for reasons unknown, it works: in 50 years of research on the rodents, none has ever spontaneously developed cancer. We might finally be zeroing in on an explanation for their tumour-dodging skills.

Of the two groups, the mole rats of Africa, which belong to a family called the bathyergids, are probably the more peculiar. Two African species – the naked mole rat and the Damaraland mole rat – are the only mammals in the world to have opted for a termite-like eusocial existence: a single queen gives birth to all other colony members.

The Asian mole rats – in the spalacid family – do not go in for this kind of unusual breeding behaviour. But they do share one thing in common with their African doppelgangers: they never develop cancer. In fact, researchers have just discovered that the Middle East blind mole rat will not develop cancer even when it is exposed to some potent cancer-causing chemicals. After three years of exposure to one of two powerful carcinogens, only one of the 20 animals studied developed any tumours.

"We've shown that whether the rats are young or old, it's almost impossible to induce cancer in them," says Aaron Avivi of the University of Haifa in Israel. By contrast, rats and mice exposed to the same chemicals developed tumours in a matter of months.

Stubborn immunity

A possible implication of the mole rats' stubborn immunity is that their cells and tissues contain substances that protect them even from some of the most powerful cancer-causing chemicals. Avivi and his colleagues are now trying to identify such substances, in an effort to find new and potent agents to combat cancer in people – and they are making progress.

The team took fibroblast skin cells from the armpits of the rats and grew them in culture alongside cancer cells, including two types each of human liver and breast cancers. The fibroblasts rapidly killed the human cancer cells. So did fluids secreted by the fibroblasts, suggesting that there's something in there of great value to combat cancer. And when he checked, Avivi found that the fibroblasts and their secretions didn't harm healthy human cells. "It was only cancer cells," he says.

As controls, fibroblasts and secretions from normal lab rats, mice, and another rodent called the spiny mouse were powerless to stop the human cancer cells growing.

When Gorbunova genetically engineered naked mole rats so that they could not make HMM-HA, they became vulnerable to cancer, suggesting that the substance is a key to protecting them.

Avivi isn't convinced that HMM-HA can explain why his Middle East mole rats do not get cancer, though. He says that the extracts from their fibroblasts do contain the sticky substance, but that in spalacids it does not seem to play a key role in the animals' natural resistance to cancer or activity against cancer cells in the lab.

Gorbunova says there are some other possible mechanisms. The Middle East mole rat cells might secrete another chemical, called beta interferon, which kills cancerous cells. But she remains convinced that the key chemical protecting both naked and blind mole rats is HMM-HA.

Avivi, meanwhile, is continuing to check for other cancer-killing chemicals that might be responsible. "Our future work is to try to find what Spalax cells secrete that only interacts with and kills cancer cells," he says.

Correction:When this article was first published on 15 August 2013, it did not explain that HMM-MA in the fibroblasts of Middle East mole rats does not seem to be significant in their resistance to cancer or activity against cancer cells.

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